Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. This proposed AD would require replacing the engine fuel shutoff valves for the left and right main tanks. This proposed AD results from a report of a failed engine start, which was caused by an internally fractured engine fuel shutoff valve. We are issuing this AD to prevent the failure of the valve in the closed position, open position, or partially open position, which could result in engine fuel flow problems and possible uncontrolled fuel leak or fire.